Argon stirring of molten steel is well known. See, e.g., U.S. Pat. No. 4,238,227 of Eugene A. Golas et al., the entire disclosure of which is hereby incorporated by reference into this specification. In this argon stirring process, low volumes of inert gas, such as argon, typically at a rate of from about 0.005 to about 0.05 cubic feet per ton of molten steel per minute are continuously introduced into the mass of molten during the rinsing period. Other flow rates are used for the alloying step of steel processing, and for the arc reheating step of steel processing.
The flow rate used during argon stirring of steel is critical. If it is too low, or too high, many problems arise including, e.g., damage to the containment vessel in which the molten steel is disposed, inclusion of impurities (such as carbon, or nitrogen) into the molten steel bath, creation of arc flaring, temperature stratification, and the like.
Even when the flow rate to the steel containment vessel is maintained at some constant level, the flow rate within the vessel may vary. This variance is often caused by factors such as leakage in the gas delivery system, back pressure variations at the plug delivering the gas into the system, plugging and/or erosion of the orifices through which the gas is flowed into the system, and the like.
The prior art has recognized that the flow rate of inert gas within the steel containment vessel is not necessarily the same as the flow rate of gas delivered to the steel containment vessel. This problem was discussed in a paper by R. L. Minion et al. entitled "Improved Ladle Stirring using Vibration Technology at Stelco Hilton Works," which was given at the 1998 Steelmaking Conference Proceedings held in Toronto, Canada in 1998. In this Minion paper, it was disclosed that ". . . there as no direct means of stir indication during reheating at these lower flow rates . . ." and, consequently, ". . . a direct method of stir detection was necessary . . ." The method proposed by the Minion paper involved ladle vibration monitoring in order to measure energy transfer to the ladle.
In the proposed Minion process, an accelerometer was magnetically attached to a ladle to detect ladle vibrations in the vertical direction. Thereafter, the output from the accelerometer was filtered to remove frequencies above 100 Hertz, and the output so filtered was displayed and evaluated to determine the extent of argon mixing taking place within the ladle.
According to the Minion process, the results obtained varied substantially for the same ladle at the same rate of stirring; according to the authors, these incongruous results might be due to ". . . bubble formation frequency at the porous plug . . ." Whatever the causes of these anomalies, the net result is that the Minion process has not met with any commercial success.
It is an object of this invention to provide an improved process for directly detecting the extent of argon gas stirring within a liquid metal container.
It is another object of this invention to monitor the extent of arc flaring which occurs during arc heating of steel and to diminish such arc flaring.